diff --git a/Makefile b/Makefile
index b9da58757a..cc167212c0 100644
--- a/Makefile
+++ b/Makefile
@@ -132,13 +132,13 @@ engine-up: engine-clickhouse-up engine-mssql-up engine-mysql-up engine-postgres-
 engine-down: engine-clickhouse-down engine-mssql-down engine-mysql-down engine-postgres-down engine-spark-down engine-trino-down
 
 fast-test:
-	pytest -n auto -m "fast and not cicdonly" --junitxml=test-results/junit-fast-test.xml && pytest -m "isolated" && pytest -m "registry_isolation" && pytest -m "dialect_isolated"
+	pytest -n auto -m "fast and not cicdonly and not isolated" --junitxml=test-results/junit-fast-test.xml && pytest -m "isolated and not slow" && pytest -m "registry_isolation" && pytest -m "dialect_isolated"
 
 slow-test:
-	pytest -n auto -m "(fast or slow) and not cicdonly" && pytest -m "isolated" && pytest -m "registry_isolation" && pytest -m "dialect_isolated"
+	pytest -n auto -m "(fast or slow) and not cicdonly and not isolated" && pytest -m "isolated" && pytest -m "registry_isolation" && pytest -m "dialect_isolated"
 
 cicd-test:
-	pytest -n auto -m "(fast or slow) and not pyspark" --junitxml=test-results/junit-cicd.xml && pytest -m "pyspark" && pytest -m "isolated" && pytest -m "registry_isolation" && pytest -m "dialect_isolated"
+	pytest -n auto -m "(fast or slow) and not pyspark and not isolated" --junitxml=test-results/junit-cicd.xml && pytest -m "pyspark" && pytest -m "isolated and not pyspark" && pytest -m "registry_isolation" && pytest -m "dialect_isolated"
 
 core-fast-test:
 	pytest -n auto -m "fast and not web and not github and not dbt and not jupyter"
diff --git a/tests/conftest.py b/tests/conftest.py
index 4d1bb23577..1f7f6d9325 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -212,11 +212,13 @@ def pytest_collection_modifyitems(items, *args, **kwargs):
         "dialect_isolated",
     }
     for item in items:
+        if "capsys" in item.fixturenames:
+            # capsys is not threadsafe, so the test must be isolated.
+            item.add_marker("isolated")
         for marker in item.iter_markers():
             if marker.name in test_type_markers:
                 break
         else:
-            # if no test type marker is found, assume fast test
             item.add_marker("fast")